Water ski



United States 3,027,575 WATER SE1 Chester H. Fortin, Tarzana, Califi, assignor to For-tin flllastics, Inc, Van Nuys, Califi, a corporation of Callorma Filed June 26, 1957, Ser. No. 663,079 3 Ciaims. (Cl. 9--31t)) This invention relates to water skis and particularly to such a ski having an improved and novel construction.

Ideally, a water ski should be in the form of an elongated, fiat body, having a broad running surface and being light weight and strong. conventionally, such skis are formed from a hardwood such as hickory which is relatively heavy. Efforts have been made to form water skis from light weight plastic materials. In general, these efforts have been unsatisfactory since, in order to achieve lateral rigidity, i.e., substantial freedom from a twisting action around the major axis of the ski, plastic skis had to be formed with a substantially greater thickness than wooden skis which added considerably to their weight.

Accordingly, one of the principal objects of the present invention is to provide a water ski utilizing light weight plastic materials which have substantial lateral rigidity.

A further object of the present invention is to provide a water ski construction having improved skiing characteristics.

A more particular object of the present invention is to provide a water ski having a novel construction which, in use, causes the formation of an air boundary layer between the ski and the water.

Other objects and advantages of the present invention will be apparent it is believed from the following detailed description of a preferred embodiment thereof when read in connection with the accompanying drawings.

FIGURE 1 is a perspective view of a water ski modified in accordance with the present invention.

FIGURE 2 is a sectional view taken substantially on the line .fZ2 of FIGURE 1.

FIGURE 3 is a sectional view of a modified version of the water slci.

Referring now to the drawings, a water ski modified in accordance with the present invention is indicated generally at 10. The ski in the form of an elongated, substantially fiat body consists essentially of a running portion 11, a long shallow shovel 12 extending from the running portion and terminating in the tip 13. A foot binding 14 is positioned on the running portion 11 and is secured to the ski by any suitable means. This construetion is conventional, the length of the shovel and position of the foot binder being determined by the characteristics and dimensions of the particular water ski to be made.

The ski is formed from an outer fabric layup 16 enclosing an inner core 17. The layup is an impregnated unidirectional woven glass fiber cloth, the fibers being oriented along the major axis of the ski. This fabric is impregnated with a synthetic polymer such as an epoxy, phenolic, polyester or resorcinol resin. The core 17, which is enclosed within and bonded to the layup 16, is formed from any light weight buoyant material, preferably balsa wood, styrofoam or cellular cellulose acetate. By this construction a light weight water ski may be formed which is not subject to the waterlogging or warping common in wooden water skis.

In order to provide lateral rigidity I have provided the ski with a concave running surface 18 extending from the end 19 to the shovel 12. By this construction the tendency for the ski to twist around its major axis is considerably reduced, allowing the ski to be used even under the most adverse conditions. This construction has a further advantage. When the skier is making a 2 turn, particularly at high speeds, a twisting torque is ap plied to the ski by the pressure of the water from below and the weight of the skier from above. The skier at tempts to position the ski at an angle to the water in order to get a bite between the ski and the water. If the ski twists along its major axis, it tends to stay parallel to the surface of the water thereby tending to cause the skier to slide rather than turn. By theme of the con' The use of the concave running surface 18 has a further and unexpected advantage. When the ski is being used, particularly at the higher speeds and in rough water, a boundary layer of air 21 is'trapped between the running surface of the ski and the water surface 22. The thickness of this boundary depends upon the radius of the concave running portion. This boundary layer acts as a cushion which reduces to an appreciable extent the slapping effect of the ski against the water, providing the skier with a smoother and less tiring ride.

As shown in FIGURE 3, the running surface may be provided with a plurality of concavities which may be desirable if a particularly broad ski is used. The use of a plurality of concavities providesincreased lateral rigidity and retains the air cushion etfcct indicated above.

In order to achieve the lateral rigidity and air cushion effect I have determined that it is necessary to provide the running surface with a concavity having a specifiediaxirnum effective radius. This maximum radius is de/ fined by the following equation:

r where: r=the radius of the concavity w=the width of the ski, and n=the number of concavities.

The radius thus defined is a maximum. Concavities having greater effective radii are too flat to achieve the desired results. As the length of the radius is decreased, the arc of the concavities increases. The minimum radius will be dependent upon the thickness of the ski, it being apparent that there must be sufficient distance between the crown 2d of the concavity and the top of the ski to permit the retention of structural strength.

he following specific example will illustrate a method of constructing a ski which is the subject of this invention. A block of balsa wood was cut to the general shape of the ski desired. it was then sanded and shaped to form an elongated body 5 feet long, 6 inches wide and 1 /8 inches thick. The running surface of the ski was then provided with a concavity extending from the end 19 to the shovel 12. From the above equation it was determined that the maximum effective radius 1' should be equal to or 36 inches. The concavity was shaped so as to have a mean effective radius equal to about 20 inches. The depth of the concavity, i.e., the distance from the plane of the running surface to the crown of the concavity was in excess of A; of an inch. The running surface corners were rounded slightly to form an are having a radius of approximately 0.1 inch to provide for the formation of a fiat spray pattern when the ski was used. The formed Patented Apr. 3, 1962' balsa wood was then soaked in water and placed into a shaped metal mold and subjected to pressure at a temperature of approximately 110 F. The mold was shaped to provide the balsa core with a shovel and tip. The core was then removed from the mold and air dried at 130 for twenty-four hours. An elongated strip of unidirectional woven glass fiber cloth was impregnated with a styrene modified polyester resin (Paraplex P-43 manufactured by Rohm & I-Iaas). The impregnated cloth was then wrapped around the ski so as to completely enclose it and the excess material cut away. The wrapped ski was then placed in a shaped mold under heat and pressure sufficient to cure the resin. After curing the ski was removed from the mold and allowed to cool. A foot binder was then secured to the top surface of the running portion. The resulting product was a strong, light weight water ski which resisted twisting and was usable at high speeds and in rough weather.

It will be apparent that other polymers may be used in forming the outer layup and that the inner core may be formed from other strong, light weight materials such as styrofoam or cellular cellulose acetate. Further, it will be apparent that skis of different dimensions having varying widths, lengths and thicknesses may be formed without departing from the present invention.

Having fully described my invention, it is to be understood that I do not wish to be limited to the precise details of the examples set forth, but my invention is of the full scope of the appended claims.

. I claim:

1. A water ski, having a major axis and a minor axis, comprising: an elongated body having a running portion, a shovel and a tip; said running portion being provided with a running surface, said body having an outer fabric layup and an inner core; said fabric layup being formed from a unidirectional woven glass fiber cloth, said fibers being oriented in a direction substantially parallel to said major axis, said cloth being impregnated with a styrene modified polyester resin; said inner core being formed from balsa wood; said running surface being provided with a concavity and a corner along either side of said concavity, the axes of said concavity and said corners being each substantially parallel to said major axis, the

radius of each of said corners being substantially uniform and equal to 0.1 inch, the said concavity being substantially uniform along the length of said running surface, the effective radius of said concavity being equal to or less than the square of the width of said ski, the width of said concavity being substantially equal to the width of said running surface.

2. In a water ski, including an elongated body having an outer layup and an inner core, the improvement comprising: a longitudinal concave running surface formed in said body, the width of the concavity being substantially equal to the width of the ski and the radius of the cross sectional arc of the concavity being equal to or less than the square of the Width of the ski, said concavity being substantially uniform along the entire length of said running surface, said running surface being provided with comers, the radii of said corners being substantially equal to 0.1 inch.

3. In a water ski, including an elongated body having an outer layup and an inner core, the improvement comprising: a longitudinal running surface having a plurality of longitudinal concavities formed therein, the sum of the widths of the concavities being substantially equal to the width of the ski and the radii of the cross sectional arcs of the concavities being equal to or less than the square of the width of the ski divided by the number of concavities squared, each of the said concavities being substantially uniform along the length of the said running surface, said running surface being provided with corners, the radii of said corners being substantially equal to 0.1 inch.

References Cited in the file of this patent UNITED STATES PATENTS 'I-Iowland June 25, 1946 Maynard et al Nov. 12, 1935 Broome Dec. 26, 1939 Rheinfrank Nov. 23, 1954 Ritter Dec. 3, 1957 Metcalfe Jan. 12, 1960 FOREIGN PATENTS France Sept. 25, 1933 

